Smart tools for quantum optics

Sample Experiments – Quantum Eraser

The quED-MI is designed in such a way that the polarisation of the photons at the input of the interferometer is diagonal (i.e. 45° between horizontal and vertical). Now we add polarisers in the two arms of the interferometer, one horizontal, one vertical. This affects the interference:

This can be interpreted in the following way: At the output of the interferometer, you can determine by the polarisation of the photon, which of the two possible paths it has taken (so-called “which-way” or “welcher-Weg” information). Thus, the interference is destroyed.

Now, we add a third polariser at the output of the interferometer. This is what happens:

The interference re-appears. Do you know why it is called the “quantum eraser”?